There are three groups of radon studies that resulted in our determination that radon does indeed cause lung cancer. Below we will review the following types of studies:
- Underground Miners
- Human Research Studies
Occupational Miner Studies
- Linear dose response relationship was found for all the occupational studies
- A 1994 NCI pooled analyses of 68,000 miners concluded that about 39% of the lung cancer deaths among smokers and 73% of the lung cancer deaths among never-smokers may have been due to their occupational radon progeny exposure
- Projecting risks to the residential setting they concluded that radon progeny may be responsible for 10 – 12% of lung cancers in smokers and 28 -31% in never-smokers.
Why Animal Studies so Important?
- Animal studies confirm radon carcinogenicity and linear dose relationship. The relationship between the amount of exposure (dose) to a substance and the resulting changes in body function or health (response). – Agency for Toxic Substances and Disease Registry
- Health effects observed in animals exposed to radon and radon decay products include lung carcinomas, pulmonary fibrosis, emphysema, and a shortening of life-span (U.S. DOE/Office of Energy Research 1988a).
- Exposure to ore dust or diesel fumes simultaneously with radon did not increase the incidence of lung tumors above that produced by radon progeny exposures alone (DOE/Office of Energy Research 1988a).
- The incidence of respiratory tract tumors increased with an increase in cumulative exposure and with a decrease in rate of exposure (NAS 1988).
Overview of Human Research Methods
Overview of Human Research Methods:
- Residential Studies
- Ecological vs. Case-Control
- Ecological: Studying a population rather than an individual.
- Case-Control: Studying individuals with a disease & comparing against individuals without the disease (control group).
- Show the number of lung cancer deaths for a region compared with substitute measures of exposure for that region.
- Showed a relationship between exposure to radon and an increased risk of lung cancer.
Flaws in Ecological Model:
- Ecologic studies do not consider information on individual smoking history.
- Ecologic studies do not consider information on individual mobility.
- Both of which are important variables in assessing radon risk
- Ecologic studies were discontinued and replaced with the more reliable case-control studies.
- Compared individuals with lung cancer (cases) to individuals without lung cancer (controls).
- Both groups compared for differences in home exposures, (using substitute measures of radon exposure). A number of these studies found an association between indoor exposure to radon and increased lung cancer risk.
- Scientists determined that when taken individually, some studies don’t have the statistical power for conclusive reporting
- For this reason, scientists decided to pool data from international studies as they are completed.
- Recent Case-Control Studies:
- Pooled studies from Europe, North America & China
- Notably: Iowa Radon Lung Cancer Study or IRLCS
- The North American Residential Radon Pooling Study
- Combined data from twenty residential studies to confirm the radon risks predicted by extensive occupational mining studies
- The studies include:
- Iowa Radon Lung Cancer Study (Epidemiology March 2005)
- European Residential Radon Pooling Study (British Medical Journal January 2005)
- By pooling the residential data, studies showed an increased lung cancer risk consistent with the predicted 12% per 2.7 pCi/L based on a linear model developed by the National Research Council.
- Notice…threshold level of cancer incidence at 2.7 pCi/L (not 4.0 pCi/L).